Hi All;

I'm retrofitting a 1980's VMC with Fanuc 6MB electronics. The retrofit is going great, Jon from Pico has been very helpful. I've hit the stage of the project were I'm reverse engineering all the sensors and relays, etc. I have Fanuc documentation but no machine documentation. Hundreds of connections! There are several recurring wire labels I don't understand. Can anyone help with what these "common" wire labels mean?

"OP" What is this? It seem to work like ground but is not Gnd
"OL" Same as above
"S11" This is used lots of places, I think it's power of some type
"R11" Same as above
"+24P" This is clearly 24 Volts but what's the P versus N?
"+24N" This is clearly 24 Volts but what's the P versus N?

Thanks!